How to use CAD block reference as a command? Where is it specifically used? Could you please provide an example? Thank you. Detailed information will be worth extra points.

This question is very simple! Let’s first talk about our common uses of external references: topographic maps and picture frames.

After we draw the drawings, we print them. For formal drawings, drawing frames are required. Usually a set of drawings uses the same kind of drawing frames, which means that some of the contents in the drawing frames are the same. If you give Paste the frame on each drawing. If the content of the frame needs to be modified, you have to modify it one by one. Sometimes, it is normal to have hundreds of drawings in a set. Think about the workload... At this time, external reference is very good . The external reference here is like this. After the drawing frame is drawn, it is saved as a separate drawing in the ordinary dwg format. Then, when a certain drawing is to be framed, the xr command brings up the external reference manager and clicks "Attach" ", find the location of the "frame", and apply the frame to the current drawing. Do the same for other drawings that need to be framed. The advantage of this is that when the content of the frame needs to be changed, you only need to change the single frame graphic, and the frames in other graphics covered by external references will automatically be changed, which is very trouble-free.

Use the form of external reference to set topographic maps. When we design roads, bridges, and housing buildings, we always have general plans and other things. We need to express the current situation, that is, the terrain, and we need to draw new information on the topographic map. The buildings and structures are equal to the topographic map, which is the base map. The topographic map is usually provided by the survey unit or other units. When printed, the topographic base map is very light and the things in it are messy. We do not want to change it, it is just used as a base map. When using a fixed background, the external reference is to attach the topographic map to the drawing you want to draw in the form of an external reference. The advantage of this is that when you draw the picture, you will not accidentally put the topographic map It has been modified. When the terrain is not displayed, since the reference terrain map is a whole (similar to a block), just click on a part of the terrain map to select the entire terrain, and delete it quickly.

The above is my personal understanding. The following is the official explanation, which can be found in the CAD help.

"Insert" menu: "External Reference"

Command line: xattach shortcut key: XR attaches the drawing as an external reference. If you attach a drawing that contains an attached external reference, the attached external reference appears in the current drawing. Attached external references, like blocks, can be nested. If another person is currently editing this xref, the attached drawing will be determined by the most recently saved drawing.

After an external reference is attached to a name, the name of the external reference will appear in the list. When an attached xref is selected in the list, its path appears in Paths.